Fibers utilized to produce woven and nonwoven textiles fall into the two broad categories: man-made (or synthetic) fibers and natural fibers. Common man-made fibers include, for example, polyester, nylon, and polypropylene, all of which are thermoplastic polymers. Such thermoplastic polymers are melt spun into filaments which can be either air formed into nonwoven textiles directly as described in U.S. Pat. No. 2,689,199, which is incorporated herein in its entirety by reference, or cut into finite length fibers (known commonly as “staple fibers”) which can be formed into threads and yarn for woven or knit textiles. In addition, staple fibers can be formed directly into randomly oriented fiber webs and subsequently bonded together by a variety of means to form a nonwoven textile fabric. Such staple fibers generally are kinked when employed in nonwoven webs.
The most widely known natural fibers are cotton, wool, and silk. Wool and silk are exclusively used for woven textiles. Cotton is the dominant fiber for woven textiles; although it also has minor utilization in nonwoven textiles. Cotton has limited use for modern nonwoven textile production due to its tendency to form fiber bundles when processed with the high speed carding typical of nonwoven production lines.
Wood pulp fibers are another type of natural fiber primarily is used for papermaking. Yet, wood pulp has a significant presence in the nonwoven textile industry when combined with man-made filament or staple fiber and the hydroentangling web bonding process. See, for example, U.S. Pat. Nos. 4,442,161 and 5,284,703, both of which are incorporated herein in their entirety by reference. Wood pulp has no direct presence in the woven textile industry. Rather, cellulose, the natural polymer that constitutes wood pulp fibers and other vegetative matter, is formed into a man-made class of filaments known as, for example, rayon (sometimes referred to as viscose), TENCEL®, lyocell, and derivatives thereof. Such man-made cellulosic fibers are used in both woven and nonwoven textiles. Such polymeric fibers are formed by chemically dissolving cellulosic matter, and spinning filaments from the cellulosic solution. For use in dry formed webs, man-made cellulosic fibers are typically crimped and cut into staple fibers. Fiber crimping is not required for wet-formed webs.
Another major category of natural fibers is bast fibers. Bast fibers are found in the stalks of the flax, hemp, jute, ramie, nettle, Spanish broom, and kenaf plants, to name only a few. Typically, native state bast fibers are 1 to 4 meters in length. These long native state fibers are comprised of bundles of individual fibers which are straight and have a length between 20 and 100 millimeters (mm). The bundled individual fibers are glued together by a class of plant resins called pectins.
Bast fibers have been used for at least 8,000 years for both woven textiles and cordage. However, such textiles and cordage were formed only with the native state bast fiber bundles. An example of a woven textile produced with flax bast fiber bundles is linen. More recently, as provided in U.S. Pat. No. 7,481,843, partially separated bast fiber is produced to form yarns and threads for woven textiles. However, yarns and threads are not suited for nonwoven fabrics.
Nonwoven fabrics comprising mixtures of wood pulp fibers and man-made fibers have high moisture absorption capabilities and can be produced by conventional papermaking procedures or other known dry or air-forming techniques. However, such products can lack sufficient strength for many applications, for example, for use as household cloths, food service wipes, and industrial machinery wipes. The strength of such products can be improved by including a bonding agent in the fiber furnish or by application of an adhesive binder to the formed web. When the strength characteristics of the web are improved, however, by use of an adhesive binder, such as a synthetic resin latex, the liquid absorption capability of the web is correspondingly decreased.
Accordingly, there is a need for a high-strength nonwoven fabric comprising a combination of natural bast fibers and synthetic fibers. It is to solving this problem the present invention is directed.